This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American
Editor's Note: William Gilly, a professor of cell and developmental biology and marine and organismal biology at Stanford University, is traveling with a group of students on board the Don José in the Sea of Cortez. They will monitor and track Humboldt squid and sperm whales in their watery habitats. This is the group's ninth blog post.
SEA OF CORTEZ—I am proud to say that I am now the world's third leading authority on squid stomach contents, and as such I'd like to share with you the results of my latest study.
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Well, perhaps not third, but something like that given that I only know of only two other people who study Dosidocus stomach contents. I am new to the world of digestive goo, to squid and to scientific research in general. I had a short stint in the Butterfly lab at Stanford, but that experiment died quickly along with the butterflies. So when I volunteered to do squid stomach analysis for my holistic biology class (my personal emphasis being on holism rather than the biology part), I figured I'd be handing someone scalpels and peering occasionally over someone's shoulder into a microscope. Aboard the Don José I soon learned that is not how projects here worked. A student's job is to figure out how to do it; a mentor's job is to watch and throw back a few cold ones with Ahab.
Luckily for me, my mentor Unai went above and beyond expectation. Unai really is the leading authority on stomach contents of Humboldt squid. He's charismatic, a lively storyteller and wears tiny shorts—qualities that inspired comments of "What a Man!" from my female cohorts. The first night we caught small squid, Unai dissected them, removing the stomachs so that I could preserve them in tiny bottles of alcohol. The largest stomach from this batch was about the size of my second toe. By the end of the night I was more than a little overwhelmed by the 28 stomachs in my possession, with not a clue what to do with them. Two days later we started reeling in the big ones, and I was able to add 12 frozen stomachs the size of Nerf footballs to my collection.
The following day we began cutting them open. Unai demonstrated, and I got ready to assume my position as scalpel holder when he soon abandoned the microscope and barked at me to " find all the interesting stuff and then we can identify it." I was flabbergasted, having no idea what I was looking for. I tentatively peered in to the microscope and saw a thousand flakes of remarkably identical crustacean pieces. I poked around for a while and then called to Unai. "Yeah, those are crustacean pieces, but unless you are a crustacean expert, we don't know what kind." Great. The real expert couldn't even identify them.
We opened another stomach, this time a big one because Unai thought it looked more promising. Inside were big white chunks and some purple material. It turned out to be the mantle and skin of a large male Dosidicus (we could tell by the mantle thickness and spermatophores). Emilie joined the cause as my partner, and I was grateful to have another clueless soul to roll my eyes at whenever I was told to find the good stuff. We spent several hours looking for parasites amongst the contents, and laughed uncontrollably every time one of us held up a glob and inquired, "Is this a parasite?" (We later realized that the short fat segmented ones that moved and the skinny things coiled inside the lining were in fact parasites, trematodes and nematodes respectively.)
Finally we finished the parasite search and moved on to the next stomach, another big one from a 78-centimeter female Dosidicus. The contents looked completely different from the previous two, a harder, drier mixture of blackness. Unai was instantly excited—the contents showed evidence of fish! Scattered amongst vertebrae (I could identify the fish vertebrae already, having seen them strung on a necklace in La Paz) and eyeballs were tiny round calciferous plates with ridges on one side. Unai proudly remarked that these were otoliths, one of three fish ear bones, and that they would be the key to identifying what species the squid were eating. We found a mess of them, 26 to be exact, in three variations. We matched the right and left ear bones and were able to determine that this particular squid had eaten at least 10 Benthosema panamense, a myctophid lantern fish and a favorite food item of Dosidicus. There was also one Bregmaceros bathymaster and two more of a species I have yet to identify. A Benthosema otolith is oval with a Pac-Man mouth, one of Bregmaceros is triangular, and the third type looks like a garden snail, body extended in front with no trailing foot. After identifying these otoliths, I felt a little more confident and was excited for Unai to show me more and tell me what animal every little piece in every stomach came from.
The next day, Unai left the boat. How was I supposed to do Unai's study without Unai? Reluctantly and not without our share of "This isn't fair!"s, Emilie and I began opening more stomachs. At first each one took several hours, but the more we looked at, the faster and more gratifying the work became. We started finding squid beaks all on our own. I got really in to it, beckoning for them to come out and coaxing them between my forceps. We even joked about an idea for a drinking game—every time you found a beak you would be rewarded with a sip of beer. It seemed like something Ricketts and Steinbeck would have done, or better yet, Unai. (Although he never drinks while working, just before and after, the sentiment is in the right place). Soon it became apparent that finding the pieces to the puzzle was reward enough. Thirty-seven stomachs later, the task that once seemed impossible was complete, a bittersweet moment.
I can't wait to go back to the Hopkins Marine Station lab, measure the otoliths and beaks so I can estimate the size of the consumed prey, and compare my results to Unai's from other places and other years. Preliminarily, I can tell you that within my sample, cannibalism seems to be on the rise, myctophid consumption is falling, and a lot more squid may be dying hungry. Of course the implications of my study should be taken in stride—I may be number "three" but I am no expert, and my methods could use refining. You can't compare a sample of 40 stomachs to Unai's 533 and not expect the results to be skewed by outliers. Nonetheless, I think it would be worthwhile to investigate what, if anything, is causing the possible myctophid shortage and to bear in mind that squid may not be inherently evil—perhaps they cannibalize only when they have to. From a selfish perspective, I can say that my experience with stomachs was absolutely worthwhile. Aside from learning how to use a microscope, make do with the materials I had, and apply scientific method, I learned to follow through, explore on my own, and see something in a new light. Knowledge that seems unattainable may be far more accessible than you think, requiring little more than curiosity, patience and creativity. Even if you don't know quite what you are looking for you can still learn a lot about it, just like me and my stomachs.
Images courtesy of Susan Shillinglaw